Technical Field
This disclosure relates to medical devices, and more particularly to medical devices that monitor the cardiopulmonary system using one or more acoustic sensors.
Discussion
Some conventional medical devices that monitor the cardiopulmonary system obtain a subject's electrocardiogram (ECG) signal from body surface electrodes. Determining the true characteristics of an ambulatory subject's cardiac cycle based on an ECG signal in this manner can be difficult. Electrical noise and electrode fall-off frequently degrade the quality of the ECG signal. In addition, the characteristics of ECG signals vary from subject to subject due to factors such as the subject's state of health and individual physiology.
Known ambulatory wearable defibrillators, such as the LifeVest® Wearable Cardioverter Defibrillator available from ZOLL Medical Corporation of Chelmsford, Mass., use four ECG sensing electrodes in a dual-channel configuration. That is, an electrical signal provided by one of the four ECG sensing electrodes is paired with the electrical signal provided by another of the four ECG sensing electrodes to form a channel. This arrangement of ECG sensing electrodes is usually suitable because in most cases it is rare that noise or electrode movement affects the entire body circumference. The dual-channel configuration provides redundancy and allows the system to operate on a single channel if necessary. Because signal quality also varies from subject to subject, having two channels provides the opportunity to have improved signal pickup, since the ECG sensing electrodes are located in different body positions.